A wide variety of compositions have been utilized as adhesives for wallpaper and related substrates, either as aqueous adhesive compositions that can be applied when required, or as a water-wettable prepasted adhesive.
The traditional methods for applying such prepasted wall coverings, however, display a tendency to absorb an excess quantity of water during soaking of the sheet before hanging, even though the process is intended to be very simple to operate. Consequently, the paper hanger has to exercise care during prewetting to prevent excess water absorption. Consequently, he must be careful to minimize the soaking time, which is usually ten to twenty seconds. In the present invention an excess amount of water is not absorbed, thus eliminating the problem of the water running down the wall and making the surface both dirty and sticky. This can be particularly desirable during, e.g., the hanging of wallpaper borders which are located either close to the ceiling or in the middle of the wall.
There is a multitude of related prior art in this well-worked technology; U.S. Pat. No. 4,476,190 and its European Application counterpart 077,618 disclose a variation of the composition which is utilized in the invention; however, the system disclosed therein relates to a mixture of water insoluble cationic and anionic polymers, both of which are cross-linked. Additionally, although the adhesive system disclosed does exhibit a small decrease in water absorption over time, it does not completely stop its absorption of water.
U.S. Pat. No. 4,713,264 discloses that water soluble adhesives can be utilized to coat wallpaper; however, at least seventy percent of the particles in the composition disclosed are crosslinked, i.e, a maximum of only thirty percent of the composition is water soluble.
U.S. Pat. No. 4,355,073 and its British counterpart, 2,054,628A disclose a water soluble polymer which is preferred for use as the anionic component of the mixture of the present invention. However, the resulting adhesive system exhibits no gel strength and the water soluble polymer is degradable by shear forces, as is pointed out in U.S. Pat. Nos. 3,247,171 and 4,059,552.
European Application 194,857 utilizes a suspension polymerization method to prepare adhesive polymers which are suitable for usage in wallpaper adhesive coating compositions and the like. Consequently, substantially all of the particles must have a particle size greater than twenty microns, which is not desirable in the emulsion polymerization methods of the present invention.
U.S. Pat. No. 4,361,452 and its foreign counterparts, European Application 8,213 and Canadian patent 1,144,290 disclose the utilization of water insoluble and water swellable polymers which are prepared by inverse emulsion polymerization and which form a wallpaper adhesive. The resulting polymers are cross-linked and the final suspension may contain a water soluble polymer which reduces the viscosity of the composition. However, this polymer must have the same polarity as the swollen polymer; the liquid suspension is supplied as a suspension of particulate polymers which are dispersed in an organic liquid.
European Application 178,127 and the previously cited U.S. Pat. No. 4,713,264 each disclose a method of water distillation suitable for use in the present invention. Also disclosed are the characteristics of the oil in the polymeric stabilizer which is added to assist the azeotropic distillation.
U.S. Pat. No. 4,487,864 and European Application 131,090 disclose a carbohydrate polymer in conjunction with a cross-linked water swellable polymer, such as a partially hydrolized cross-linked polyacrylamide, which is suitable as a wallpaper adhesive.
European Application 159,132 discloses a layered adhesive coating in which the first layer is a cross-linked, anionic polymer which swells only in an alkali media, while the second layer is an aminoalkyl-containing, linear, low molecular weight cationic polymer.
Mixtures of cross-linked anionic polyacrylamide and water soluble cationic polymers are disclosed in British patent 1,376,392. The resulting mixture exhibits improved adhesion when compared to the aforementioned anionic polymer.
Unfortunately, all of these wallpaper adhesive systems absorb an undesirable amount of water during excess soaking of the sheet before hanging, thereby requiring the wallpaper hanger to exercise care during the wetting process, even though the process of applying the wallpaper is intended to be very simple to operate. Accordingly, there has arisen a need for an adhesive composition which when soaked will absorb water only for a short period of time, after which significant further water absorption substantially ceases. Additionally, the adhesive imparts a hydrophilic character to the coated article, thereby enabling it to adhere to a variety of substrates such as glass, cellulose and the like. The blends of the invention can also be utilized in such diverse environments as photographic films, separation membranes, surgical implants, soft contact lenses, and as a grease resistant film.
In addition to the aforementioned advantages, it is desireable to utilize an adhesive composition which can be fabricated in a particular desired blend at the site of application and can also be used in applications where water retaining is desirable, such as in sandy soils, as well as in applications such as enhanced oil recovery, hydraulic fracturing of subterrane formations, and as a viscosity builder.